This invention relates to semiconductor devices and more specifically relates to a novel lateral conduction superjunction MOSFET device.
MOSFET superjunction devices are well known and are disclosed in U.S. Pat. Nos. 4,754,310 and 5,216,275 and in a publication entitled xe2x80x9cSimulated Superior Performance of Semiconductor Superjunction Devicesxe2x80x9d by Fujihara and Miyaska in the Proceedings of 1998 International Symposium on Semiconductor Devices and ICs, pages 423 to 426. Such superjunction devices have required deep trenches or sequentially deposited and diffused P and N epitaxially layers of silicon. Further, the operational characteristics of prior superjunction devices have not been optimized.
In accordance with a first feature of the invention, a lightly conductive Pxe2x88x92 substrate is provided, and an Nxe2x88x92 epitaxial layer and then a Pxe2x88x92 epitaxial layer are grown on the Pxe2x88x92 substrate. Laterally elongated and spaced trenches are formed from the top of the Pxe2x88x92 epitaxial region and extend down and slightly into the Nxe2x88x92 substrate. The trenches define Pxe2x88x92 mesas between them. An Nxe2x88x92 diffusion liner is then diffused into the walls and bottom of the trenches. The trenches are then filled with silicon dioxide insulation. The Nxe2x88x92 diffusion liner has a resurf concentration of 1E12 ions per cm2 over the full exposed N-trench area. The Pxe2x88x92 pillars have a concentration of 2E12 ions/cm2.
In other embodiments of the invention, the Pxe2x88x92 epi layer can be formed on an SOI (Silicon on Insulator) substrate.
The novel structure of the invention provides a number of advantages over prior art devices:
1. A shallower trench is needed to fabricate the device. Thus, a 15 micron deep trench can be used in place of a prior art 35 micron trench for a 600 volt device.
2. A denser structure can be made, using a 1 micron pitch. Since pitch is proportional to on-resistance RDSON the reduction of pitch is very desirable.
3. Since the device is a lateral conduction device, it will have a reduced gate charge Qg which is essential to many applications.
4. The novel structure of the invention lends itself to the integration of plural devices in a common chip, for example, a bridge circuit can be integrated into a single chip.
5. The device can act as a high side switch when the Nxe2x88x92 layer is designed to support the rail voltage between source and substrate. High side devices, low side devices and control circuitry can then be integrated into the same silicon.